JP3550177B2 - Image processing device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an image processing apparatus that performs color image processing of color photographs, paintings, and the like.
[0002]
2. Description of the Related Art For color printing and the like, image processing apparatuses that perform color image processing using a computer have been developed. Such a color image processing apparatus can perform color editing on a screen, such as specifying a target color to be changed and a color after the change and performing hue conversion.
[0003]
[Prior art]
FIG. 8 shows a conventional image processing apparatus.
In FIG.
Reference numeral 200 denotes an image before conversion.
[0004]
Reference numeral 201 denotes an image block before conversion, which is, for example, a set of 8 × 8 pixels.
Reference numeral 200 ′ denotes an image after conversion.
[0005]
201 ′ is an image block after conversion.
205 is an image processing apparatus.
A conversion instruction unit 206 instructs hue conversion such as designation of a hue to be converted (for example, conversion of a red hue to a yellow hue).
[0006]
210: an image data input unit for inputting image data of each pixel of the image 200. Each pixel has coordinates (L ^* , a ^* , b ^* ) in the uniform color space coordinate system. L ^* represents lightness, a ^* and b ^* represent colors (hue / saturation).
[0007]
Reference numeral 211 denotes a hue conversion unit that converts a color (a ^* , b ^* ) in the L ^* a ^* b ^* coordinate system into a hue H in the Munsell coordinate system (described later), and converts the hue of the input image data into a hue. It is determined whether or not the conversion is included in the specified hue area. If the conversion is included in the specified hue area, the converted hue H is rotated to obtain the converted hue H ′. , Hue H ′ are converted into colors (a ^* ′, b ^* ′) in the a ^* b ^* coordinate system.
[0008]
An image data output unit 212 outputs the converted image data.
As shown in the configuration of FIG. 8, the conventional image processing apparatus converts only the hue, and the brightness is not changed before and after the conversion.
[0009]
FIG. 9 is an explanatory diagram of hue conversion of a conventional image processing apparatus.
FIG. 9A is an explanatory diagram of hue conversion of a conventional image processing apparatus.
Assuming that the hue before the change of the operator's instruction is Horg, the hue angle is Rorg, the hue after the change is Hchg, and the hue angle is Rchg, H ′ after rotation with respect to H before rotation is H = Hchg− (Horg−H). X (Rchg / Rorg).
[0010]
[Problems to be solved by the invention]
The problem to be solved by the invention will be described with reference to FIG.
In FIG. 9B, the a ^* axis represents hue (saturation increases as a ^* increases), and the ordinate represents lightness L ^* . FIG. 9B shows the distribution of the lightness of the yellow hue, and shows that the lightness of the yellow hue is distributed as shown in the figure, and that the lightness is not uniformly distributed in the entire yellow hue space.
[0011]
The converted hue H ₀ ′ in FIG. 9A is a yellow hue, and if it is converted to the coordinate Y in FIG. 9B, it is in the yellow lightness distribution area. The converted hue is natural, but if it is converted to Y ′, it becomes unnatural because it has a lightness that does not actually exist.
[0012]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing apparatus that automatically adjusts lightness to lightness that is not unnatural according to a converted hue.
[0013]
[Means for Solving the Problems]
FIG. 1 shows the basic configuration of the present invention.
In FIG.
Reference numeral 1 denotes an image processing device.
[0014]
Reference numeral 2 denotes an image data input unit for inputting image data before conversion.
An image data output unit 4 outputs the converted image data.
Reference numeral 5 denotes a conversion instructing unit for designating a hue to be converted and a hue after the conversion.
[0015]
Reference numeral 10 denotes a hue conversion unit for converting the hue of the image data.
Reference numeral 11 denotes a brightness conversion unit which converts the brightness of the image data with reference to the brightness adjustment table 12.
[0016]
Reference numeral 12 denotes a brightness adjustment table that associates the brightness before adjustment with the brightness after adjustment so that the converted hue is adjusted to a non-natural brightness. The correspondence between the brightness before the adjustment and the brightness after the adjustment is performed by, for example, using a conversion formula or a conversion table in which the brightness before the adjustment and the brightness after the adjustment are associated.
[0017]
[Action]
The operation of the basic configuration of the present invention shown in FIG. 1 will be described.
The image data input unit 2 inputs image data before conversion for each pixel. The hue conversion unit 10 determines whether or not the hue of the input pixel is included in the hue of the conversion-designated area, and if the hue of the input pixel is included in the hue area for which the conversion is specified, the specified hue Convert to
[0018]
The brightness conversion unit 11 determines the brightness (luminance) of the pixel whose hue has been converted, refers to the brightness adjustment table 12, and refers to a conversion formula or conversion data of the brightness of the converted hue. Then, the conversion is performed according to the conversion formula or conversion table of the brightness.
[0019]
The image data output unit 4 outputs the converted hue and brightness image data.
According to the present invention, since the hue-converted image data is converted into a natural lightness determined according to each hue, an apparently natural converted image can be obtained.
[0020]
【Example】
FIG. 2 is a diagram showing the configuration of the embodiment of the present invention. 2 ^L * ^a * ^{b *} coordinate system coordinates ^{(L *, a *, b} *) of the ^(a *, ^{b *)} performs color conversion of hue angle H (0 to 360 °) the (H conversion) the An example configuration in the case is shown.
[0021]
In FIG.
Reference numeral 40 denotes an RGB data input unit, such as an image scanner or an image pickup device.
[0022]
A color conversion unit 41 converts the RGB data into lightness and hue (L ^* , a ^* , b ^* ) in the L ^* a ^* b ^* coordinate system.
Reference numeral 42 denotes a color conversion unit that converts the lightness and hue (L ^* , a ^* , b ^* ) of the L ^* a ^* b ^* coordinate system into RGB data or YMC data (data for print output). It is.
[0023]
43 is a display.
44 is a printing device.
An image processing device 50 converts the hue and brightness of image data.
[0024]
Reference numeral 51 denotes an image data input unit.
Reference numeral 52 denotes an image data holding unit which holds image data before conversion and image data after conversion.
[0025]
Reference numeral 52 'denotes pre-conversion image data.
52 "is image data after conversion.
Reference numeral 54 denotes an image data output unit.
[0026]
55 is a conversion instruction unit.
Reference numeral 60 denotes a hue conversion unit.
Reference numeral 61 denotes a brightness conversion unit.
[0027]
Reference numeral 62 denotes a brightness adjustment table.
70 represents image data (L ^* , a ^* , b ^* ) before conversion.
Reference numeral 71 denotes H-converted image data (H, L ^* ).
[0028]
Numeral 72 denotes coordinates (H ′, L ^* ) obtained by rotating the hue H in the Munsell coordinate system and performing hue conversion.
Reference numeral 73 denotes Munsell coordinate system image data (H ′, L ^* ) whose brightness has been converted with reference to the brightness adjustment table 62.
[0029]
73 'is image data (H, L ^* ) that has not been subjected to hue conversion.
Numeral 74 is obtained by converting (H ', L ^* ) into (L ^* ', a ^* ', b ^* ') in the L ^* a ^* b ^* coordinate system.
[0030]
The operation of the configuration of FIG. 2 will be described later.
FIG. 3 is an explanatory diagram of the relationship between hue and maximum lightness.
FIG. 3 (a) shows the relationship between hue and maximum lightness in a graph, with reference to a standard color chart and a color table, finding the lightness value of the largest saturation in each hue. FIG. 3B is a table showing the relationship between the hue and the maximum lightness.
[0031]
As shown in the graph of FIG. 3A and the table of FIG. 3B, the relationship between the hue and the maximum brightness is not uniform, but differs depending on the hue. Therefore, the hue-converted lightness also needs to be converted in consideration of the maximum value of the hue before and after the hue conversion.
[0032]
For example, consider a case where hue H = 92 is changed to hue H = 358. Hue H = 92 has the maximum lightness 184. On the other hand, the hue H = 358 is the maximum lightness 79. Therefore, in the present invention, for example, when the hue H = 92 is changed to the hue H = 358, the lightness of the converted hue is also determined according to the maximum lightness in consideration of the maximum values 184 and 79 of the lightness. Convert it.
[0033]
FIG. 4 is an explanatory diagram of a method for creating a brightness adjustment table according to the present invention.
FIG. 4A shows the case of the conversion formula.
In the H conversion from lightness L (hereinafter, lightness is also represented by L in H conversion) to lightness L ', the maximum lightness 255 is converted to the maximum lightness 255, and the minimum lightness 0 (black) is converted to the minimum lightness 0, and the hue is converted. The lightness L0 and L1 are experimentally obtained in advance so that the color of the image is naturally expressed. Then, for L0 and L1, (1) if L ≦ L0, L ′ = (L1 / L0) × L, (2) if L> L0, L ′ = 255 − ｛(L1 / L0) × (255-L)} to convert L into L ′. Note that L0 and L1 differ depending on the hue.
[0034]
FIG. 4B is a table showing L ′ for L of 0 to 255 in the conversion formula of FIG. 4A. The brightness conversion is calculated by the above conversion formula, or a conversion table is created in which the brightness L before conversion is associated with the brightness L ′ after conversion, and conversion is performed according to the conversion table. In the case of using the conversion table, the processing speed is increased.
[0035]
The conversion formula or conversion table in FIG. 4 is created for each hue or hue group.
FIG. 5 is a diagram showing an example of the brightness adjustment table of the present invention.
FIG. 5A shows a modification method 1 in the case of linear conversion (similar to FIG. 4A). L0 and L1 are experimentally obtained so that the converted lightness is natural. If the lightness L before the change is 0 ≦ L ≦ L0, the brightness is converted according to the equation of the graph k1, and if L0 <L ≦ 255, the brightness is converted according to the equation of the graph k2. The graph may be converted into a conversion table and converted according to the table.
[0036]
(B) is a case of performing non-linear conversion. As shown in the figure, L before change is converted into L 'after change by a conversion formula represented by a non-linear graph. A graph may be used as a conversion table, and conversion may be performed according to the table.
[0037]
(C) shows a case where a highlight point or a gray point is changed in the nonlinear conversion.
The solid line (k1) is for changing the gray point to a brighter one, and the dotted line (k2) is for changing the highlight point. The graph may be converted into a conversion table and converted according to the table.
[0038]
The operation of the embodiment of the present invention shown in FIG. 2 will be described.
The color conversion unit 1 (41) receives the RGB data from the RGB data input unit 40 and converts the RGB data into coordinates (L ^* , a ^* , b ^* ) in the L ^* a ^* b ^* coordinate system. The image processing device 50 inputs the image data converted by the color conversion unit 1 (41) for each pixel, and performs hue conversion and brightness conversion.
[0039]
In the image processing device 50, the image data input unit 51 extracts the image data converted into the L ^* a ^* b ^* coordinate system from the color conversion unit 1 (41) and stores the image data in the image data holding unit 52.
[0040]
Next, the operation of the hue / lightness converter will be described with reference to FIG. 6 (see FIG. 2).
S1 The color changing unit 60 determines whether all the pixels have been extracted. If all the pixels have been extracted, the process proceeds to S8, and if not, the process proceeds to S2.
[0041]
S2, S3 The hue conversion unit 60 extracts the pixels (L ^* , a ^* , b ^* ) of the image data from the image data holding unit 52. The extracted image data (L ^* , a ^* , b ^* ) (70) is H-converted to obtain H-converted image data (H, L ^* ) (71).
[0042]
S4, S4 ′ It is determined whether or not H is the target area, and if it is out of the H area, it is converted to the original (L ^* , a ^* , b ^* ) (74), and the converted image of the image data holding unit 52 The data is stored as data 52 ". If it is within the target area, the process proceeds to S5.
[0043]
The image data (71) subjected to S5H conversion is rotated to obtain coordinate data (H ', L ^* ) (72) after rotation.
In this process, if the hue before the change of the operator's instruction is Horg, the hue angle is Rorg, the hue after the change is Hchg, and the hue angle is Rchg (see FIG. 9), H ′ after rotation with respect to H before rotation is H = Hchg− (Horg−H) × (Rchg / Rorg)
[0044]
S6 The brightness conversion unit 61 refers to the hue conversion formula or conversion table corresponding to H ′ in the brightness adjustment table 62 by using the conversion unit H ′, and performs conversion after conversion based on L ^* (L in the conversion adjustment table). Find the lightness L ^* .
[0045]
S7 The image data (H ′, L ^* ) of the Munsell coordinate system in which the hue and the lightness are converted are converted into the image data (L ^* ′, a ^* ′, b ^* ′) of the L ^* a ^* b ^* coordinate system. The converted image data 52 ″ is stored in the image data holding unit 52.
[0046]
S8 After processing all image data, the image data output unit 54 outputs the converted image data to the color conversion unit 2 (42).
The color conversion unit 2 (42) converts the data into RGB data and outputs the data to the display 43. Further, the data is converted into YMC data and output to the printing device.
[0047]
FIG. 7 shows an embodiment of the hue conversion unit of the image processing apparatus of the present invention.
L ^* a ^* b ^* coordinate system of ^a *, hue ^{b *} range taken by the when the 0 to 255 each area to be converted in advance ^(a *, ^{b *)} from the ^{(a * ', b *'} ) By preparing a conversion table and performing conversion from (a ^* , b ^* ) to (a ^* ′, b ^* ′) with reference to the hue conversion table, the processing can be speeded up.
[0048]
FIG. 7 shows an embodiment of the hue converter in such a case.
In FIG.
Reference numeral 61 denotes a brightness conversion unit.
[0049]
Reference numeral 62 denotes a brightness adjustment table.
Reference numeral 80 denotes a hue conversion unit.
81 is input image data.
[0050]
An area determination unit 82 determines whether or not the input image data 81 is within the designated conversion area.
A hue conversion table reference unit 83 refers to the hue conversion table 84 when the image data is inside the conversion area, and obtains the converted hue.
[0051]
Reference numeral 84 denotes a hue conversion table which holds the converted hues (a ^* ', b ^* ') corresponding to the hues (a ^* , b ^* ) before the conversion as a reference table.
Reference numeral 85 denotes the converted image data. However, if the image data (L ^* , a ^* , b ^* ) (81) has a hue outside the conversion area, it is the same as the image data (L ^* , a ^* , b ^* ) (81) that is not converted.
[0052]
In the configuration of FIG. 7, the hue conversion unit 80 takes in the image data (L ^* , a ^* , b ^* ) (81) from the image data holding unit (not shown (see FIG. 2)).
The area determination unit 82 determines whether the captured image data is within the designated conversion area, and notifies the hue conversion table reference unit 83 of the determination result. If the captured image data (L ^* , a ^* , b ^* ) (81) is within the area designated for conversion, the hue conversion table reference unit 83 refers to the hue conversion table 84 to convert the image of the hue to be converted. The data (a ^* ', b ^* ') is taken out, the image data (L ^* , a ^* 'b ^* ') (85) is obtained, and transferred to the brightness converter 61. If the conversion is outside the designated area, the captured image data (L ^* , a ^* , b ^* ) (81) is transferred to the brightness conversion unit 61 as it is.
[0053]
The brightness conversion unit 61 refers to a brightness conversion formula or conversion data of a brightness adjustment table 62 corresponding to the hue of the received image data, obtains conversion data L ^* 'of brightness L ^* , and obtains image data (L ^* ', a ^* , B ^* ) or (L ^* ', a ^* ', b ^* ') to the image data holding unit.
[0054]
【The invention's effect】
According to the present invention, when changing the color of the image data in the image processing apparatus, the operator simply specifies the color before the change and the color after the change, and easily obtains the natural lightness according to the converted hue. Color can be obtained. Therefore, it becomes easy to obtain an appropriate color in the color editing process. Further, by using a conversion table in which conversion data is associated with hue conversion and lightness conversion, it is possible to perform high-speed hue conversion and lightness adjustment processing.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of the present invention.
FIG. 2 is a diagram showing a configuration of an embodiment of the present invention.
FIG. 3 is an explanatory diagram of a relationship between hue and maximum lightness.
FIG. 4 is a diagram illustrating a method of creating a brightness adjustment table according to the present invention.
FIG. 5 is a diagram illustrating an example of a brightness adjustment table according to the present invention.
FIG. 6 is a diagram showing a flowchart of the operation of the hue / lightness converter of the present invention.
FIG. 7 is a diagram showing an embodiment of a hue conversion unit in the image processing device of the present invention.
FIG. 8 is a diagram illustrating a conventional image processing apparatus.
FIG. 9 is an explanatory diagram of hue conversion of a conventional image processing apparatus.
[Explanation of symbols]
1: Image processing device 2: Image data input unit 5: Conversion instruction unit 10: Hue conversion unit 11: Lightness conversion unit 12: Lightness adjustment table

Claims (1)

An image processing apparatus for converting image data represented by a uniform color space system L ^* a ^* b ^* ,
A brightness adjustment table that manages, for each hue, a conversion table that associates the value of the lightness L before conversion with the value of the lightness L ′ after conversion,
Means for calculating hue H from (a ^* , b ^* ) of input image data (L ^* , a ^* , b ^* ) represented by L ^* a ^* b ^* ;
Means for determining whether or not the hue H is to be changed;
Means for determining a converted hue H ′ when the hue H is to be changed;
Means for obtaining the converted lightness L ^* 'from the lightness adjustment table using the converted hue H' and the lightness L ^* before conversion;
Means for obtaining L ^* a ^* b ^* -based image data (L ^* ', a ^* ', b ^* ') from the converted hue H' and the converted lightness L ^* ';
Means for outputting (L ^* ', a ^* ', b ^* ') as the converted image data.

Images